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BQ40Z50-R2: SMBUS line is pulled down

Ran Aloni
Expert 2386 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50-R1

Hi all,

I'm testing a new circuit with BQ40Z50-R2.

I can communicate freely with a different board with BQ40Z50-R1 on it with the exact same schematics (but different components arrangement).
I can see the SMBUS signal on the scope and everything is fine.

when I connect to the new board I made with BQ40Z50-R2, I see a flat 0.7V on both lines.

so far I tested:
1) correct voltage on all cell pins, BAT and VCC are powered.
2) SMBD and SMBC are reaching the IC pins in a good manner.
3) shorted the PACK+ and BAT+ as EVM circuit suggests to start the IC action.
4) when nothing is connected to the EV2300, I can see the voltage on its SMBUS data line of 3.3V trying to write and waiting for answer.
this means that it is pulled down to 0.7 as soon as connected to the board.

what can be the reason?

what can I test to understand this issue?

best regards, Ran

  • 0
    TI__Mastermind 25955 points
    Hi Ran,

    To determine if the problem follows the part or the board, please remove the bq40z50-R2 on your new board and place it on a known good board, preferably a known good EVM. If the part functions properly on the known good EVM, you have isolated the issue to the new board.

    Please let me know the results of this swap.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Expert 2386 points

    Thanks Bryan,

    the number 0.7V should have light the "Idea Bulb" sooner...

    the ESD diodes were placed in reverse.

    communication works now.

    thanks!